There have been proposed so far various optical elements and optical measurement devices used for measuring a specific component in a living body tissue or a solution. For example, International Publication No. 01/58355 A1 has proposed a method for obtaining information on inside living body by bringing a living body tissue into contact with an optical element having grooves and using the difference in refractive indexes between the grooves and the living body tissue.
FIG. 8 is a structural diagram of a conventional optical element having grooves as proposed in International Publication No. 01/58355 A1. The arrows in FIG. 8 show paths of the light outputted from the light source 44. The light (arrow X in FIG. 8) entered into the side faces 42a of the grooves 42 in the optical element 41 is outputted from the side faces 42b, after passing through the living body tissue 48. Information on the living body tissue can be obtained by detecting the outputted light with a detector or the like.